SPOROPHYTE. 33 
divide only transversely, and give rise to the three rows of cells of the 
stalk (fig. 176). The four wall-cells form the walls of the sporangium. 
The archesporial cell at once cuts off four tapetal cells (figs. 161, 162), 
one on each of its faces, beginning on the sides. Each tapetal cell divides 
into four by anticlinal walls. The archesporial cell then divides nearly 
vertically into two, and the tapetum divides periclinally into two layers 
(fig. 163). The exact relation in time of the divisions of archesporium 
and tapetum is not constant (figs. 164, 166). From this time onward the 
archesporial cells divide exactly synchronously, though in different planes, 
first into four (figs. 165, 166), then into eight, and finally into sixteen. 
As soon as the sixteen spore mother-cells are formed the tapetum begins to 
degenerate (figs. 167, 170). Its walls dissolve, and the cytoplasm forms 
a vacuolated mass, but the nuclei persist until the spores are acquiring 
their definite walls (fig. 168). The spore mother-cells, at first in a solid 
mass (fig. 167), enlarge rapidly and separate from one another. Their 
nuclei especially increase to a relatively great size (fig. 170). The chro- 
matin now lies in innumerable fine granules. Then a long, fine, and 
tangled chromatin thread is organized, and synapsis ensues. This must 
be a lengthy stage, as it is frequently and easily found. Emerging from 
synapsis, a heterotypic division occurs. The two resulting nuclei at once 
divide again, and spindle fibers are formed between all four of the daughter 
nuclei. Across the fibers cell-walls are laid down. The spores remain 
together in fours until their walls are thickened. They separate before 
the final sculpturings are formed on the outside. Thus the spores always 
show a tetrahedral angle. The sculpturings are irregular lines and lumps 
of brown substance (figs. 174, 175). All stages in the formation of 
sporangia and spores may be found in a single collection of material from 
newly unfolded fronds (e. g., Loch Raven, Maryland, at base of a steep hill 
facing north, June 4, 1905). Meanwhile the wall of the sporangium has 
also reached its mature size and structure. The sides consist of very thin, 
broad cells, about eleven on each side. The right and left sides are nearly 
identical (figs. 171, 172). The annulus runs from the stalk up one edge 
and over the top of the sporangium and about one-quarter of the way 
down the other edge. Its cells, 18 or 19 in number, are cubical and 
are heavily lignified on all except the outer walls. The mouth of the 
sporangium, or point of rupture, lies between two long, narrow, slightly 
thickened cells (sometimes two such cells on one or the other lip) about 
midway between the end of the annulus and the stalk. Similarlong, narrow 
cells, three to five in number, but with thin walls, fill up the space above 
and below the mouth. At maturity the whole sporangium and contents 
dry out, and the spores are hurled away as described for another fern by 
Atkinson (1894). The annulus tends to straighten, and it does so, slowly 
opening the mouth of the sporangium and tearing the walls nearly straight 
across their whole width. It bends far around backward until the head 
